1. Field of Invention
This invention relates to solar water heating devices. More particularly, the invention relates to devices that combine heat collection and hot water storage in a single xe2x80x9cpassivexe2x80x9d unit known as an xe2x80x9cintegrated collector/storagexe2x80x9d or xe2x80x9cICSxe2x80x9d unit.
2. Description of Related Art
Solar energy holds great promise for heating domestic water for residences. However, installation costs for solar water heating systems have typically been too high for economic viability. Solar collection systems of moderate efficiency can typically supply 40 to 70% of annual residential water heating requirements using only 30 to 40 square feet of roof surface. A combination of installation difficulties and high component costs cause paybacks to exceed ten years for these relatively small systems. Available systems divide into active and passive categories. An active system requires a pump and electrical source to circulate water through a rooftop solar collector component, returning the heated water to an insulated water container. A passive system does not require a pump to circulate water or other heating fluid. Integral collector/storage (ICS) units offer particular promise for reducing costs because they minimize the total surface area of system components, in addition to eliminating moving parts and electrical connections.
ICS designs have been in use for many years. Traditional xe2x80x9cbreadboxxe2x80x9d ICS units place a cylindrical metal tank under a glazing. The tank is typically under city water pressure. When the sun shines, water passing through the tank is heated on its way to fixtures or an auxiliary water heater. While many such breadbox units have been site-built, several U.S. manufactured units were widely marketed in the 1970""s and early 1980""s until federal and state tax subsidies were no longer available. These units used either stainless steel or xe2x80x9cglass-linedxe2x80x9d steel tanks placed in insulated boxes. Plastic glazings were used as top covers to admit solar energy and limit tank losses to the environment during non-solar conditions. The tanks for xe2x80x9cbreadboxxe2x80x9d units typically contain 30 to 60 gallons of water. The concentrated weight of the units, due to the water, further complicated installation because roof reinforcement was often required. While overnight tank losses limit ICS xe2x80x9csolar fractionxe2x80x9d compared to active systems with well-insulated indoor tanks, the lower installed cost, and the elimination of energy costs for pumping, give ICS units an advantage in many applications.
Although less costly than active systems, available ICS systems are still too expensive for significant market penetration in either new home or retrofit applications. Two ICS units currently being marketed resolve the concentrated weight problem by using a xe2x80x9cparallel tubexe2x80x9d design that distributes the pressurized water relatively uniformly in a rectangular box. For example, a 3xe2x80x2 by 8xe2x80x2 ICS unit places 6 or 8, 3xe2x80x3 to 4xe2x80x3 diameter horizontal tubes side-by-side, joining them at alternating ends to create a serpentine flow pattern from cold water entering one end of the bottom tube to solar-heated water leaving the tube at the top. However, these simple, durable units are expensive to manufacture due to the high cost and weight of the large copper tubes needed to contain pressurized water without corrosion.
Unnecessarily high manufacturing costs of known ICS systems also result from the design of the enclosure that surrounds the parallel tube array. A flat rectangular box with 4xe2x80x3 internal tubes is typically fabricated from 7xe2x80x3 tall aluminum perimeter extrusions. A flat xe2x85x9xe2x80x3 thick glass cover sheet is held to the perimeter members with a smaller aluminum extrusion forming a channel that includes a small rubber channel gasket strip that captures the glazing. The corners of the aluminum extrusions are mitered and secured with corner clips. The lower outsides of the main extrusion profile have features that accommodate aluminum clips for securing the ICS unit to the roof rack that is secured to the roof. An aluminum sheet bottom panel is also supported by the perimeter extrusions. The bottom and walls are typically lined with about 1xe2x80x3 of rigid isocyanurate foam insulation that is cut from larger panels. All of the enclosure components are relatively expensive, and require substantial factory labor to prepare and assemble.
Although the uniform weight distribution of available ICS units somewhat reduces installation difficulties, these xe2x80x9cparallel tubexe2x80x9d ICS units still require substantial on-site labor to install. Furthermore, a unit will typically weigh at least 300 pounds before filling with water, requiring a crane or boom truck to lift into place. The units are usually supported above the roof surface on racks that require four connection points through the roof. Such rack-mounting is customary to allow the roof to xe2x80x9cbreathxe2x80x9d under the collector, where debris and moisture might otherwise collect and rot, thereby accelerating roof degradation. Because the spacing of roof structural members may vary, securing the rack often becomes a custom project. Also, the required piping penetrations are not at the four support bolt locations, resulting in at least six different roof penetration locations, each requiring careful sealing and/or flashing to prevent leakage. Such mounting methods also risk damage to the roof structure, since bolts driven downward into roof structural members (now more heavily loaded) may weaken the structural members.
Current breadbox solar water heaters also have aesthetic liabilities associated with their size and rack mounting. One of the damaging legacies from the failed solar heating movement of the 1970""s and early 1980""s is that roof-mounted solar heating equipment is not particularly attractive. Units 8xe2x80x3 thick supported on racks another 4xe2x80x3 above the roof have high visibility, and look out of place on many residential roofs.
For these and other reasons, there is a need for a low cost, lower profile ICS solar water heater that can easily and quickly be installed on both new or existing residences, that minimizes the danger of water leakage through the roof, and that brings solar water heating into an affordable budget range for households in sunny climates throughout the world.
The present invention is directed to an integrated collector/storage (ICS) solar water heater. The apparatus and methods of the invention include the use of molded polymer technology to reduce the cost of materials and the number of parts that must be assembled to manufacture the ICS unit. The invention also includes support and connection features that eliminate the need for a mounting rack, significantly reducing the cost of installation labor, and reduces or minimizes the likelihood of leakage at mounting surface penetration points.
In an exemplary embodiment of the invention, the apparatus and methods of the improved ICS solar water heater include a rotationally-molded fluid container (xe2x80x9cwater boxxe2x80x9d) with an internal heat exchanger, a glazing subassembly, and a mounting/connection hardware kit. In one embodiment, the heat exchanger contains pressurized water in small, thin-walled copper tubes that are surrounded by solar heated water in the water box which is under xe2x80x9catmospheric pressurexe2x80x9d. Because the water box is not pressurized beyond atmospheric pressure, the walls of the water box may be relatively thin, as compared to existing ICS units, thereby decreasing weight, reducing production costs and improving heat transfer. In the exemplary embodiment, the water box comprises two essentially parallel sheets, joined by spaced xe2x80x9cthrough-connectsxe2x80x9d, and four sides providing a closed perimeter. The water box may be produced by rotational molding.
In an exemplary embodiment of the apparatus and methods of invention, the molded fluid container, or water box, is designed to rest directly on a mounting surface, such as a roof surface by using a water box having a ribbed bottom with vent passages that are open along their lower edge. The space formed between the ribs may be closed at their upper ends to prevent debris from being deposited under the water box. This feature provides for ventilation between the water box and the mounting surface to remove moisture.
In an exemplary embodiment of the apparatus and methods of invention, the water box is tapered from a narrower profile at the bottom of the water box to a thicker profile at the top of the water box. The taper provides more internal space in the top portion of the water box, where the heat exchanger is located, and reduces the length of the through-connects at the bottom portion of the water box, where water pressure is highest.
In an exemplary embodiment of the apparatus and methods of invention, the water box may include a metal underside strut located in a vent passage of the water box formed by the ribs disposed on the bottom surface of the water box. The strut facilitates connection of the ICS unit to a single structural member on a mounting surface, thereby simplifying layout and connections by eliminating the need to consider varying spacings of particular structural members, such as roof rafters or trusses, for example. The strut may be integrated with mounting hardware, such as upper and lower brackets and mounting plates that are pre-secured to the mounting surface thereby facilitating the rapid and secure mounting of the ICS unit. For example, in an exemplary embodiment, the brackets surround a framing member thus avoiding weakening the member by driving large fasteners such as lag bolts into the framing member.
In yet another exemplary embodiment of the apparatus and methods of the invention, the glazing subassembly includes a formed polymer glazing with integral ribs and a rim that minimize the size of the rigid perimeter extrusions that strengthen the lower glazing edge, hold two flexible sealing strips, and facilitate securing the glazing subassembly to the water box and mounting points.
In an exemplary embodiment of the apparatus and methods of the invention, mounting hardware is provided that connects to the strut disposed on the underside of the water box and facilitates all connections between the mounting surface and the ICS unit along the vertical centerline of the unit. In an exemplary embodiment, the hardware for mounting the ICS unit on a roof includes below-roof brackets and above-roof mounting plates. The below-roof brackets surround a rafter or truss framing member and provide connection means to the above-roof plates. In addition to providing a secure connection that does not damage the framing member, the top bracket also holds and aligns the supply and return water lines for connection to the heat exchanger stub-outs of the water box. The upper above-roof mounting plate also includes a closed-cell foam gasket to provide a seal around roof penetrations. The lower above-roof mounting plate also provides a seal around roof penetrations.
These and other features and advantages of this invention is described in or are apparent from the following detail description of various exemplary embodiments of the systems and methods according to the invention.